Search Results (36)

To develop a high-efficiency process for removing phosphorus (P) from metallurgical grade silicon, a novel method of combining Si-Cu solvent refining and CaO-CaF₂-CaCl₂ slag treatment was investigated through simultaneously re-constructing P-containing phases of CaCu₂Si₂ in the Si-Cu alloy and Ca₃P₂ in the slag. After acid leaching, P-containing phases can be eliminated, whereupon high-purity silicon could be recovered from the Si-Cu alloy. The effect of slag components and alloy composition on the P removal efficiency was studied systematically. When the Si-40 wt.% Cu alloy is treated with 20 wt.% CaO-32 wt.% CaF₂-48 wt.% CaCl₂ slag for 60 min at 1400 °C, the P removal efficiency reaches 90.1%. Furthermore, the mechanism of enhanced P removal was also discussed. It was indicated that a silicothermal reduction reaction occurred between CaO and Si, which caused Ca to migrate into the alloy and precipitate the P-containing CaCu₂Si₂ in the Si-Cu alloy. Simultaneously, P in silicon is reduced to P³⁻ at the slag–alloy interface, forming Ca₃P₂ in the slag, thereby establishing a dual-path purification mechanism. Hence, this study provides new insight into silicon high-efficiency purification from economical and practical considerations. Full article

Rare-earth molten-salt electrolysis slag contains a substantial quantity of rare-earth elements, rendering it a valuable secondary resource for rare-earth recovery. To achieve the efficient recovery of praseodymium (Pr), neodymium (Nd), lithium (Li), and fluorine (F) from rare-earth molten-salt electrolysis slag, this paper proposes an atmospheric alkaline leaching method. The leaching efficiency of Nd, Pr, F (95.02%), and Li (95.87%) can be reached at a NaOH concentration of 80%, a reaction temperature of 180 °C, a reaction time of 2 h, and an alkali to slag ratio of 3:1. Leaching efficiency kinetic analysis shows that the leaching processes of fluorine and lithium are both controlled by interfacial chemical reactions, with apparent activation energies of 59.06 kJ/mol and 57.33 kJ/mol, respectively. The mineral phase transformation and morphological analysis were studied by X-ray diffractometer and scanning electron microscope. The results indicated that rare-earth fluoride (REF₃) reacts with sodium hydroxide to form rare-earth hydroxide (RE(OH)₃) and soluble sodium fluoride (NaF), while LiF is converted into LiOH and enters the liquid phase. High-efficiency separation was achieved by washing with water, avoiding high-temperature energy consumption and the problem of fluorine-containing waste gas. Full article

Spent rare earth molten salt electrolytic slag (REMES) needs to be recovered not only because of its economic value of rare earth elements (REEs), lithium, and fluorine, but also for the environmental benefits. Vacuum distillation has many advantages, such as a short process and less wastewater. Aiming to find an environmentally friendly method to recover REEs, this research studied the challenges in recovering REMES by vacuum distillation and the solutions to handle these obstacles. Distillation experiments for the raw material were initially implemented and XRD, XPS, DSC, and SEM methods were used to investigate the phase changes of REMES, thus discovering that oxide impurities could transform REF₃ into REOF, which significantly affected the REEs recovery. Only 42.04% of the REEs could be evaporated at 1573 K and 0.1 Pa for 4 h with 99.99% of LiF. To tackle this issue, a fluorination pretreatment was proposed. NH₄HF₂ was utilized to transform oxide impurities, RE₂O₃, and REOF to fluorides with almost no waste gas released, significantly improving the recovery efficiency of the REEs, which was 86.23%. Therefore, this paper proposes this fluorination–vacuum distillation method, which has a short process to recover REF₃ from REMES efficiently with almost no wastewater or gas released. Full article

Fast high-temperature gas-phase reactions occurring in the limited space of the arc cavity in the submerged arc welding (SAW) process limit the study of specific gas-phase behaviours. A low-temperature experimental method is applied to investigate gas-phase reactions in the reaction of oxy-fluoride slag with Al-Fe-Ni metal powders. The presence of nano-strands in the slag cavities confirms the vaporisation and re-condensation of gasses. Ti is the main element in nano-strands, although some nano-strands also contain Al-Mg-Si-Na oxy-fluoride. Nano-strand end-caps contain Mn-Fe-Si fluoride, and some contain Ni. The Ni in nano-strand end-caps is sourced from the added Ni powder and indicates gas-phase transfer. The Ti in the nano-strands is sourced from the flux. Themochemistry calculations identify KAlF₄, TiF₃, NaAlF₄, SiF₄, AlF₃, SiF₃, and Na in the gas phase. Increased Al reaction results in decreased TiF₃ in the gas phase, likely due to the displacement of Ti from TiF₃, resulting in the gas-phase transfer of Ti from the flux. Comparative diffusion flux calculations support Ti nano-strand formation via the vaporisation of TiF₃ and the re-condensation of Ti. The low-temperature simulation experiment applied here can be used to study the gas reaction behaviour in the reaction of oxy-fluoride flux with metal powders. Full article

Fast-neutron reactors are an important representative of Generation IV nuclear reactors, and due to the unique structure and material properties of fast reactor fuel, traditional mechanical cutting methods are not applicable. In contrast, laser cutting has emerged as an ideal alternative. However, ensuring the stability of optical fibers and laser cutting heads under high radiation doses, as well as maintaining cutting quality after irradiation, remains a significant technical challenge. Here, we study the performance changes in optical fibers exposed to a total radiation dose of 10⁵ Gy, focusing on power transmission and thermal characteristics. By integrating irradiated optical fibers with irradiated laser cutting heads, simulated cutting experiments on the hexagonal tubes of spent fuel from fast reactors (fast reactor simulation assembly) were conducted. Critical cutting quality parameters, including kerf width, surface roughness, and slagging length, were analyzed. The results indicate that, while the power transmission performance of irradiated optical fibers shows slight degradation, its impact on cutting quality is minimal. High-quality cutting can still be achieved under optimized parameters. This study confirms the feasibility of laser cutting technology in high-radiation environments and provides essential technical support for its application in nuclear fuel reprocessing. Full article

Recycling and reusing industrial waste and by-products are topics of great importance across all industries, but they hold particular significance in the metal industry. Aluminum, the most widely used non-ferrous metal globally, generates considerable waste during production, including dross, salt slag, spent carbon cathode and bauxite residue. Extensive research has been conducted to recycle and re-extract the remaining aluminum from these wastes. Given their varied environmental impacts, recycling these materials to maximize residue utilization is crucial. The components of dross, salt slag, and bauxite residue include aluminum and various oxides. Through recycling, alumina can be extracted using processes such as pyrometallurgy and hydrometallurgy, which involve leaching, iron oxide separation, and the production of alumina salt. Initially, the paper will provide a brief introduction to the generation of aluminum residues—namely, dross, salt slag, and bauxite residue—including their environmental impacts, followed by an exploration of their potential applications in sectors such as environmental management, energy, and construction materials. Full article

The relationship between slag structure and viscosity is studied, employing Raman spectroscopy for the five-component slag system of MnO-SiO₂-CaO-Al₂O₃-MgO and its subsystems. This study aims to investigate the influence of variations in slag composition on viscosity, which is crucial for optimizing industrial processes. Based on industrial slag compositions produced in a silicomanganese submerged arc furnace, 17 slags with a fixed content of MnO of 10 wt% are synthesized with varying contents of SiO₂ of 33 to 65 wt%; CaO within the range of 14 to 40 wt%; and fixed contents of Al₂O₃ and MgO of 17 and 6 wt%, respectively. The slag compositions are divided into four groups, ranging from low basicity (0.38) to high basicity (0.80), with each group containing the four slag systems of MnO-SiO₂-CaO, MnO-SiO₂-CaO-Al₂O₃, MnO-SiO₂-CaO-MgO, and MnO-SiO₂-CaO-Al₂O₃-MgO, with fixed basicity. Additionally, a five-component composition with the lowest basicity of 0.28 is considered. Raman spectroscopy measurements are performed in the wavenumber range of 200 to 1200 ${\mathrm{cm}}^{-1}$ using a green source laser with a 532 nm wavelength. The high-wavenumber region of the Raman spectra (800 to 1200 ${\mathrm{cm}}^{-1}$) is deconvoluted to quantitatively investigate the effect of each oxide on the slag structure and the degree of polymerization (DOP) of the silicate network. Results indicate that measured NBO/T increases with increasing basicity, demonstrating a reduction in DOP of the silicate structure. This depolymerization effect is more pronounced in slags containing Al₂O₃ compared to those without it. In a group of slags with similar basicity, the substitution of SiO₂ with Al₂O₃ leads to further depolymerization. In contrast, substituting CaO with MgO has little effect on the silicate structure in slags without Al₂O₃ but causes depolymerization in slags containing Al₂O₃. To study the relationship between structure and viscosity, viscosity data obtained from FactSage are used as reference values. The predictions of slag viscosity using the Raman-structure model and the NBO/T viscosity model are then compared to the FactSage results. The adjustable parameters of the Raman-structure model are re-determined using the FactSage data for the studied slag compositions. The NBO/T viscosity model employs both calculated NBO/T values from the slag compositions and measured NBO/T values from the deconvolution results. The findings of this study reveal good agreement between the predictions of the Raman-structure model and the FactSage viscosity data. Full article

The study object was slag from the Balkhash copper smelter, obtained by re-melting anode mud containing nonferrous metals. The process flow for processing these slags includes sintering with Na₂SO₄, Na₂CO₃, and coal, followed by soda-alkaline leaching of the sinter and extraction of metals from the solution into marketable products. Since sintering is the main operation providing high selectivity, the composition of the products of this process was studied. The main transformations during sintering were determined, and the optimal parameters were identified. The structures of slags and sintered materials obtained during the experiments were studied by electron-probe microanalysis. Sintering was performed at 600–800 °C. The best results for sulphidization of slag components were obtained at 800 °C; a further increase in temperature leads to the smelting of sinter particles and slows down sulphidization. The optimal quantities of additives, based on the weight of the slag, are Na₂SO₄—45%, Na₂CO₃—15%, and reducing agent—41%, with a sintering time of 2 h. These conditions enable the sulphidization of non-ferrous metals in the slag to the entire depth of the polymetallic globules. The distinct concentration of harmful impurities (Ni, As, and Sb) was observed in the fine structure of the polymetallic globules. Full article

The submerged arc welding (SAW) process is operated at high temperatures, up to 2500 °C, in the arc cavity formed by molten oxy-fluoride flux (slag). These high arc cavity temperatures and the complex interaction of gas–slag–metal reactions in a small space below the arc render the study of specific chemical interactions difficult. The importance of gas phase reactions in the arc cavity of the SAW process is well established. A low-temperature (1350 °C) experimental method was applied to simulate and study the vaporisation and re-condensation behaviour of the gas species emanating from oxy-fluoride flux. Energy dispersive X-ray spectroscopy (EDX) analyses and reaction thermochemistry calculations were combined to explain the role of Al as a de-oxidiser element in gas phase chemistry and, consequently, in nano-strand formation reactions. EDX element maps showed that the nano-strands contain elemental Ti only, and the nano-strand end-caps contain Co-Mn-Fe fluoride. This indicates a sequence of condensation reactions, as Ti in the gas phase is re-condensed first to form the nano-strands and the end-caps formed from subsequent re-condensation of Co-Mn-Fe fluorides. The nano-strand diameters are approximately 120 nm to 360 nm. The end-cap diameter typically matches the nano-strand diameter. Thermochemical calculations in terms of simple reactions confirm the likely formation of the nanofeatures from the gas phase species due to the Al displacement of metals from their metal fluoride gas species according to the reaction: yAl + xMF_y ↔ xM + yAlF_x. The gas–slag–metal equilibrium model shows that TiO₂ in the flux is transformed into TiF₃ gas. Formation of Ti nano-strands is possible via displacement of Ti from TiF₃ by Al to form Al-fluoride gas. Full article

The engineered artificial mineral (EnAM) lithium aluminate (LiAlO₂) is a promising candidate for the recycling of lithium from slags, which can originate from the reprocessing of batteries, for example. Derivatives of the natural product Punicine (1-(2′,5′-dihydroxyphenyl)-pyridinium) from Punica granatum have been proven to be effective switchable collectors for the flotation of this mineral as they react to light. In the present study, three Punicines were added to a planetary ball mill before grinding LiAlO₂ to particle sizes suitable for flotation. We investigated the influence of Punicine and two derivatives with C10 and C17 side chains on the grinding results at different grinding times and conditions as well as on the yields in flotations. SEM images of the particles, IR and ICP–OES measurements provided insights into the Punicine–particle interactions. They showed that Punicines not only prevent the formation of hydrophilic and thus undesirable lithium aluminate hydroxide hydrate (LiAl₂(OH)₇ ▪ x H₂O) surfaces in this process, as is unavoidable in aqueous flotation without this pretreatment, they also prevent the undesired release of lithium cations into the aqueous phase. Due to considerable hydrophobization of the particle surface of LiAlO₂, nearly quantitative recovery rates of this engineered artificial mineral are achieved using the process described here. Full article

The steel manufacturing industry is one of the most concentrated anthropogenic carbon-emitting point sources that is still expected to increase further each year. Moreover, steel slags are also generated at a rate of 10–20% of the total crude steel production. The possibility to valorize both the flue gases and steel slags through mineral carbonation has garnered the spotlight in recent research on waste valorization and sustainable steel production practices. Mineral carbonation of steel slags leads to the stable adsorption of carbon dioxide onto the surface of the steel slags. Nonetheless, it is essential to assess whether the environmental benefits resulting from the mineral carbonation process would outweigh the environmental burdens associated with the transformation and carbonation processes. To this end, this study aims to illustrate the potential environmentally friendly industrial waste valorization pathway by performing life cycle assessment (LCA) to obtain the environmental impacts of carbonated steel slags. The environmental impacts are calculated by the ReCiPe 2016 midpoint methodology. Furthermore, contribution analysis for the carbonated slag production is provided. This study also illustrates a comparison of steel slag carbonation with pure carbon and flue gases by means of scenario analysis. The results of this study should provide insights into the possibility of employing mineral carbonation on industrial wastes in the metallurgical sector as well as highlight the possible areas of improvement for prospective scale-ups. To this end, the results of this study could contribute to the improvement of the environmental sustainability of the steel manufacturing sector. Full article

The depletion of the ore reserves in the world necessitates the search for secondary sources such as waste products (tailings and slag). The treatment and cleaning up of such secondary sources also has a positive impact on the environment. A smelter in Namibia we examined had historic slag which accumulated over decades of its operating life, thus posing the challenge of how best to collect representative samples to evaluate and propose viable methods of recovering contained metals. In this study, analytical and mineralogical characterization of the slag was performed using X-ray fluorescence (XRF) analysis, atomic absorption spectrometer (AAS), ICP-OES, scanning electron microscopy energy dispersive spectroscopy (SEM-EDS) analysis, and optical microscopy analysis. The chemical analyses showed that the metal values contained in the slag were mainly copper, lead, and zinc whose average contents were approximately 0.35% Cu, 3% Pb, and 5.5% Zn. About 10.5% Fe was also contained in the slag. Germanium was detected by scanning electron microscopy, but was however below detection limits of the chemical analysis equipment used. Based on the results, approximate conditions under which the different slag phases were formed were estimated and the recovery routes for the various metals were proposed. Analysis by both optical and scanning electron microscopy revealed that Zn and Fe occurred mainly in association with O as oxides, while Cu and Pb were mainly associated with S as sulphides. The slag consisted of three different phases, namely the silicate phase (slag), metallic phase and the sulphide phases. The phases in the slag were mainly silicate phases as well as metallic and sulphide phases. It was observed that the metallic and sulphide phases were dominant in the finer size fractions (−75 µm) whereas the sulphide phase was also present in the coarser size fractions (+300 µm). An important finding from the microscopy examination was that the sulphide phases were interstitial and could be liberated from the slag. This finding meant that liberation and subsequent concentration of the sulphide phases was feasible using conventional processing techniques. Full article

The scope of this work is to improve the SAW process understanding and present an improved description of the SAW process in terms of gas-slag-metal reactions with alloy powder and Al powder additions. The scope does not include the materials properties of the weld metal. The latter may easily be optimised in the future by changing the weld metal chemistry once the process reactions of different element powders in SAW are understood. Aluminium as de-oxidiser element was applied to SAW to lower the oxygen partial pressure in the process. The results show the Al-Ni-Cr-Co-Cu alloyed weld metal total oxygen content was reduced to 257 ppm O, compared to the base case weld metal at 499 ppm O, made with the same flux and no metal powder additions. Thus, the aluminium that was added as a de-oxidiser element to the SAW process effectively lowered the original flux-induced partial oxygen pressure, both in the arc cavity and at the interface of the molten flux–weld pool phases. This partial oxygen pressure lowering effect of Al also prevents oxidation of Cr, preventing loss of Cr to the slag. Carbon steel was alloyed to 3.9% Al, 4.8% Ni, 4.9% Cr, 4.8% Co, 4.7% Cu at 62% Al yield, 76% Ni yield, 77% Cr yield, 75% Co yield, 74% Cu yield. SEM (scanning electron microscope) work on the three-dimensional (3D) post-weld slag sample show dome cavities with 3D rounded structures embedded in the dome cavity walls, as well as shards and nano-strands on the dome cavity walls. The 3D structures indicate vapour formation and re-condensation of oxy-fluorides. The novel application of the EERZ (effective equilibrium reaction zone) model simulates the mass transfer effects in the SAW process. This model is novel because it is the first model used to calculate the gas-slag-metal phase chemistry changes in SAW as a function of welding time. The novel SAW process modification of adding Al de-oxidiser powder with alloying element powders of the unique combination of Co-Cr-Co-Ni-Al was successfully applied. The results confirm that the gas phase and its reactions must be included in the interpretation and modelling of SAW process metallurgy. Full article

Cement has long been recognized as an energy- and emission-intensive construction material. Cement production has recently experienced significant growth despite its high energy consumption, resource usage, and carbon emissions. This study aims to assess and compare the life cycle assessment (LCA) of traditional Portland cement (CEM I) to those of three blended cement types (CEM II/B-L, CEM II/B-V, and CEM III/A), which assume mature technologies for reducing carbon emissions in South Africa, using LCA in compliance with ISO/TS 14071 and 14072. As its scope, the study employs the “cradle to gate” method, which considers the raw materials, fuel usage, electricity, transportation, and clinkering stages, using 1 kg of cement as the functional unit. The LCA analyses were performed using SimaPro 9.1.1.1 software developed by PRé Consultants, Amersfoort, Netherlands and impact assessments were conducted using the ReCiPe 2016 v1.04 midpoint method in order to compare all 18 impact categories of 1 kg of cement for each cement type. The assessment results show reductions in all impact categories, ranging from 7% in ozone depletion and ionizing radiation (CEM II/B-L) to a 41% reduction in mineral resource scarcity (CEM III/A). The impacts of global warming were reduced by 14% in the case of CEM II/B-L, 29% in the case of CEM II/B-V and 35% in the case of CEM III/A. The clinkering process was identified as the primary cause of atmospheric impacts, while resource depletion impacts were attributed to raw materials, fuels, and electricity processes, and toxicity impacts were primarily caused by raw materials. Alternative materials, like fly ash and ground granulated blast furnace slag (GGBFS), can significantly help to reduce environmental impacts and resource consumption in the cement industry. Full article

Reducing the costs of repairing concrete structures damaged due to the appearance of cracks and reducing the number of people involved in the process of their repair is the subject of a multitude of experimental studies. Special emphasis should be placed on research involving industrial by-products, the disposal of which has a negative environmental impact, as is the case in the research presented in this paper. The basic idea was to prepare a mortar with added granulated blast furnace slag from Smederevo Steel Mill and then treat artificially produced cracks with a Sporosarcina pasteurii DSM 33 suspension under the conditions of both sterile demineralized water and water from the Danube river in order to simulate natural conditions. The results show a bio-stimulated healing efficiency of 32.02% in sterile demineralized water and 42.74% in Danube river water already after 14 days. The SEM images clearly show calcium carbonate crystals as the main compound that has started to fill the crack, and the crystals are much more developed under the Danube river water conditions. As a special type of research, microscopic images of cracks were classified into those with and without the presence of bacterial culture. By applying convolutional neural networks (ResNet 50), the classification success rate was 91.55%. Full article